The invention relates to an anti-theft device for a motor vehicle, of the type comprising a bolt restored by a spring to the position for locking an element essential to the motion of the vehicle, a lock comprising a stator and a rotor which is actuated by a coded key and which in the course of its rotation causes the bolt to be drawn back into the unlocked position, in opposition to the action of the said spring, and a safety device interacting with the key in order to prevent the bolt from returning to the locked position as long as the key has not been at least partly extracted from the rotor.